1. Field of the Invention
The present invention relates to an invention of a method of recording information on optical recording media and reproducing or retrieving the information therefrom.
2. Description of the Prior Art
Hitherto, for a method of recording time-sequential signals such as sound signal, video signal or data bits with a high density, so called optical video disk recording is known. The art of the known optical video disk is that light modulated by a signal strikes a plastic thin film and causes polymerization corresponding to the light intensity, the disk then being chemically etched and metal-plated. Then by using the plated disk as a stamper, a plastic thin film is pressed to form thickness changes, i.e. small pits, on it. For reproducing the recorded signal a laser light is irradiated on the disk, thereby interference of light between a light reflected at the surface of the thin film and a light reflected at the bottom of the same occurs, so that intensity of the resultant reflection light changes responding to the change of thickness or depth of the pits of the thin film.
A second prior art is disclosed in the Gazette of Japanese Unexamined Patent Publication Sho 52-114306 for the art of reflection type video disk. In this art, a light absorbing recording film is disposed on a substrate disk with a light reflecting film inbetween and the light absorbing recording film is at least partly evaporated or distorted at absorption of a laser light beam modulated by a signal thereby to form micro-pits.
The first prior art has an advantage that prerecorded disks can be easily mass-produced by mechanical pressing, but its disadvantage is that reproduction of the signal immediately after recording is not possible. The second prior art has not yet become into practical use because of difficulty of the forming a protection coating on its recording film due to the necessity of evaporation thereof.
Still another prior art is disclosed in U.S. Pat. No. 3,665,425 which uses a thin film of chalcogen compound as a recording media. Recording of a signal on the thin film is made by irradiating the film by a stronger laser light beam, so that the irradiated part is heated almost close to its melting point thereby to form voids at the irradiated portions. Reproduction of the signal is made by irradiating such a weaker laser light thereon so as not to further change the thin film, thereby detecting difference of light intensities between a light reflected from the portion including voids and a light reflected by the other portion. Due to light scattering at voids, the light reflected from the portion including the voids is weaker than that from the other part, and therefore a change of light intensity is produced. This art has the disadvantages that its output signal namely change of reflected light, is small; and also that detection of the scattered light is difficult because of very weak light intensity.